The following are the officially supported architectures for Debian GNU/Linux
lenny:

Intel x86 ('i386')

Alpha ('alpha')

SPARC ('sparc')

PowerPC ('powerpc')

ARM ('arm')

MIPS ('mips' (big-endian) and 'mipsel' (little-endian))

Intel Itanium ('ia64')

HP PA-RISC ('hppa')

S/390 ('s390')

AMD64 ('amd64')

ARM EABI ('armel')

You can read more about port status, and port-specific information for your
architecture at the Debian port
web pages.

2.1. What's new in the distribution?

This new release of Debian again comes with a lot more software than
its predecessor etch; the distribution includes over
7700 new packages, for a total of over 23200
packages. Most of the software in the distribution has been updated:
over 13400 software packages (this is
72% of all packages in etch).
Also, a significant number of packages (over 3100,
17% of the packages in etch) have
for various reasons been removed from the distribution. You will not
see any updates for these packages and they will be marked as
'obsolete' in package management front-ends.

With this release, Debian GNU/Linux updates from X.Org 7.1 to X.Org 7.3.

Debian GNU/Linux again ships with several desktop applications and
environments. Among others it now includes the desktop environments
GNOME
2.22[1], KDE
3.5.10, Xfce 4.4.2, and
LXDE 0.3.2.1+svn20080509.
Productivity applications have also been upgraded, including the
office suites
OpenOffice.org
2.4.1 and KOffice
1.6.3 as well as
GNUcash 2.2.6,
GNUmeric 1.8.3 and
Abiword 2.6.4.

Updates of other desktop applications include the upgrade to
Evolution 2.22.3
and Pidgin 2.4.3 (formerly known as Gaim). The
Mozilla suite has
also been updated:
iceweasel
(version 3.0.6) is the unbranded
Firefox
web browser and
icedove
(version 2.0.0.19) is the unbranded
Thunderbird
mail client.

Among many others, this release also includes the following software updates:

Package

Version in 4.0 (etch)

Version in 5.0 (lenny)

Apache

2.2.3

2.2.9

BINDDNS Server

9.3.4

9.5.0

Cherokee web server

0.5.5

0.7.2

CourierMTA

0.53.3

0.60.0

Dia

0.95.0

0.96.1

Ekiga VoIP Client

2.0.3

2.0.12

Exim default email server

4.63

4.69

GNU Compiler Collection as default compiler

4.1.1

4.3.2

GIMP

2.2.13

2.4.7

the GNU C library

2.3.6

2.7

lighttpd

1.4.13

1.4.19

maradns

1.2.12.04

1.3.07.09

MySQL

5.0.32

5.0.51a

OpenLDAP

2.3.30

2.4.11

OpenSSH

4.3

5.1p1

PHP

5.2.0

5.2.6

PostfixMTA

2.3.8

2.5.5

PostgreSQL

8.1.15

8.3.5

Python

2.4.4

2.5.2

Tomcat

5.5.20

5.5.26

The official Debian GNU/Linux distribution now ships on 4 to 5 binary
DVDs
or 28 to 32 binary CDs
(depending on the
architecture) and 4 source DVDs or 28 source
CDs. Additionally, there is a
multi-archDVD, with a
subset of the release for the amd64 and
i386 architectures, along with the source code. For
the first time, Debian GNU/Linux is also released as Blu-ray
images, also for
the amd64 and i386
architectures, along with the source code.

Debian now supports Linux Standards Base (LSB) version 3.2.
Debian 4.0 did support version 3.1.

2.1.1. Package management

The preferred program for package management from the command line is
aptitude, which can perform the same package
management functions as apt-get and has proven to be
better at dependency resolution. If you are still using
dselect, you should switch to aptitude as the official front-end for package
management.

For lenny an advanced conflict resolving mechanism has been
implemented in aptitude that will try to find the
best solution if conflicts are detected because of changes in
dependencies between packages.

2.1.2. The proposed-updates section

All changes to the released stable distribution (and to oldstable)
go through an extended testing period before they are accepted
into the archives. Each such update of the stable (or oldstable)
release is called a point release. Preparation of point releases
is done through the proposed-updates mechanism.

Packages can enter proposed-updates in two
ways. Firstly, security-patched packages added to
security.debian.org are automatically added to
proposed-updates as well. Secondly, Debian GNU/Linux
developers may upload new packages directly to
proposed-updates. The current list of packages
can be seen at http://ftp-master.debian.org/proposed-updates.html.

If you wish to help test updates to packages before they are
formally added to a point release, you can do this by adding the
proposed-updates section to your
sources.list:

The next time you run aptitude update, the
system will become aware of the packages in the
proposed-updates section and will consider them
when looking for packages to upgrade.

This is not strictly a new feature of Debian, but one that has not
been given much exposure before.

2.2. System improvements

There have been a number of changes in the distribution that will benefit new
installations of lenny, but may not be automatically applied on upgrades from
etch. This section gives an overview of the most relevant changes.

SELinux priority standard, but not enabled by default

The packages needed for SELinux (Security-Enhanced Linux) support have been promoted to priority
standard. This means that they will be installed by
default during new installations. For existing systems you can install SELinux
using:

# aptitude install selinux-basics

Note that SELinux support is not enabled by default.
Information on setting up and enabling SELinux can be found on the Debian Wiki.

New default syslog daemon

The package rsyslog takes
over as default system and kernel logging daemon for Debian 5.0,
replacing syslogd and klogd.
With stock logging rules, it can be used as a drop-in replacement; if
you have custom rules, you should migrate them to the new configuration
file, /etc/rsyslog.conf.

Users upgrading from etch need to install rsyslog and remove sysklogd manually. The default syslog daemon is
not replaced automatically at the upgrade to lenny.

Better support for UTF-8

A number of additional applications will be set up to use UTF-8 by
default or have better UTF-8 support than before. See at http://wiki.debian.org/UTF8BrokenApps about
applications that still have difficulties in handling UTF-8.

Identification of the release's revision

Starting from Lenny, /etc/debian_version
will indicate the revision number of the debian release (5.0, then
5.0.1, etc.)

This also means that you should not expect this file to be constant
throught the release lifetime.

The Debian Wiki
has some additional information about changes between etch and lenny.

2.3. Major kernel-related changes

Debian GNU/Linux 5.0 ships with kernel version 2.6.26 for all
architectures.

There have been major changes both in the kernel itself and in the
packaging of the kernel for Debian. Some of these changes complicate
the upgrade procedure and can potentially result in problems while
rebooting the system after the upgrade to lenny. This section
gives an overview of the most important changes; information on how
to work around potential issues is included in later chapters.

2.3.1. Changes in kernel packaging

Binary firmware for some drivers moved to non-free

Some drivers load binary firmware into the device they are
supporting at run time. While this firmware was included in the
stock kernel in previous releases, it has now be separately
packaged in the non-free section. If you want to continue to
use these devices after reboot, make sure the required firmware
is present on the installed system. See section 6.4 of the
Installation
Manual for details.

New OpenVZ kernel flavor

Debian GNU/Linux 5.0 provides pre-built kernel images for OpenVZ, a
second virtualization solution to go alongside the Linux-VServer
support included in etch. Advantages of OpenVZ include
support for live migration, at the expense of a slightly higher
overhead.

Kernel x86 packages unified

In previous releases there was a special -k7 kernel
flavor for 32-bit AMD Athlon/Duron/Sempron processors. This variant
has been dropped; the single single flavor -686
now handles all AMD/Intel/VIA 686 class processors.

Where possible, dummy transition packages that depend on the new packages have
been provided for the dropped packages.

2.4. Emdebian 1.0 (based on Debian GNU/Linux lenny 5.0)

Lenny now contains the build tools for Emdebian which allow Debian
source packages to be cross-built and shrunk to suit embedded ARM
systems.

The Emdebian 1.0 distribution itself contains prebuilt ARM packages
sufficient to create root filesystems that can be customised for
specific machines and machine variants. Kernels and kernel modules
need to be provided separately. Support for armel and i386 is under
development.
See the Emdebian
webpage for further information.

2.5. Netbook support

Netbooks, such as the Eee PC by Asus, are now supported by
Debian. For the Eee PC, have a look at the eeepc-acpi-scripts. Also, Debian
features a new Lightweight X11 Desktop Environment, lxde, which is beneficial for
netbooks or other computers with relatively low performance.

2.6. Java now in Debian

The OpenJDK Java Runtime Environment openjdk-6-jre and Development Kit
openjdk-6-jdk, needed
for executing Java GUI and Webstart programs or building such
programs, are now in Debian. The packages are built using the
IcedTea build support and patches from the IcedTea project.